1. Technical Field
The present invention relates to antennas, and, more particularly, relates to coils for feeding multi-band antenna structures.
2. Description of the Related Art
A helical coil for coupling to an extendible, straight-wire antenna is known in the art, by, for example, U.S. Pat. No. 4,121,218 to Irwin et al. The helical coil and extendible straight-wire are dimensioned for resonance in a particular frequency band of a portable radio such as a cellular telephone.
As different analog and digital cellular telephone systems are promulgated throughout the world, antennas corresponding to each of the different cellular systems are known. Cellular telephone subscriber users who travel through different systems or who use a cellular telephone in a geographical area with more than one system, desire a single cellular telephone usable on more than one system. Communication on differing bands of frequencies in the same radio is therefore desired. Because antennas of different bands for the same cellular telephone could likely be inconvenient for a user, a single antenna structure capable of operation at more than one band is desired.
New designs of cellular telephones are evolving to satisfy user convenience. Most users appreciate small packages which are convenient to carry and use. A multi-band antenna structure of a compact design, while achieving low manufacturing costs, is desired.
Achieving both a compact and multi-band antenna structure capable of the high gain performance of prior single band antenna structures has been difficult. Known antenna structures optimized for maximize gain in one band have design characteristics yielding sub-optimal gain at other bands. Antenna gain performance equal to or better than existing single-band antennas is desired for all bands in a single, compact, antenna structure. Such has not heretofore been possible before the present invention which will be explained below with reference to the accompanying drawings.